Hereinafter, the background art and its problems will be described.
Generally, a method of manufacturing a coil spring largely includes a cold spring coil manufacturing method and a hot spring coil manufacturing method.
In the cold coil spring manufacturing method, a purchased oil-tempered wire or induction-treated wire having a desired material diameter is coiled in the form of a coil spring using a cold coiling machine to manufacture a coil spring. In the hot coil spring manufacturing method, a wire rolled in a material processing factory or a rod-shape material is processed into a coil spring material having a diameter and length required for a coil spring, and then the coil spring material is heated to a predetermined temperature in a heating furnace, coiled in the form of a coil spring using a coiling machine, quenched and then tempered to manufacture a coil spring.
The hot coil spring manufacturing method is described in more detail as follows.
Generally, in order to manufacture a coil spring through the hot coil spring manufacturing method, first, a coil spring material is linearized to have a diameter identical with the material diameter of a coil spring to be manufactured, and then the linearized coil spring material is cut to a desired length through a material processing process and then heated to a temperature of 950-1000° C. in a heating furnace, and then the heated coil spring material is coiled in the form of a coil spring using a coiling machine, quenched and then tempered to manufacture a coil spring.
However, the above conventional hot coil spring manufacturing method is problematic in that coil spring materials having the same material diameters as those of coil springs to be manufactured must be respectively prepared in order to manufacture coil springs having various material diameters, and in that environment-friendly coil springs cannot be manufactured because fossil fuels are generally used in a heating furnace.
Further, the above conventional hot coil spring manufacturing method is problematic in that it takes a lot of time to pass a spring coil material through a heating furnace until the spring coil material is heated, so that the spring coil material is decarbonized and is formed on the surface thereof with an oxide film, thereby exerting a negative influence on coil spring quality.
Meanwhile, recently, since coil springs are strongly required to be light in order to reduce the fuel consumption rate of automobiles, high-stress coil spring materials containing high-priced special metals have been developed. However, there are also problems in that the production cost of a coil spring is increased, and thus it is also very difficult to decrease the fuel consumption rate of automobiles through the decrease in weight of the automobile.